Project Summary/Abstract Acute kidney injury (AKI) significantly increases the risk of developing progressive kidney fibrosis and chronic kidney disease (CKD). Macrophages play complex roles in AKI, with classically activated proinflammatory macrophages initially serving for clearance of apoptotic cells and debris after injury, and alternatively activated reparative macrophages promoting tubule repair followed by either egress or apoptosis of the macrophages in the event of adaptive repair. However, persistent parenchymal inflammation or more severe injury leads to maladaptive kidney repair. Our recent publication and preliminary data has shown that failure to achieve tubular repair after unilateral ischemia/reperfusion injury (U-IRI) leads to abnormal intrarenal profibrotic macrophage and dendritic cell accumulation beyond day 10. The expression of potential macrophage homing and profibrotic activation signals in unrepaired kidneys reveals high-level expression of macrophage chemoattractant protein-1 (Mcp1), predominantly by macrophages, along with sustained expression of chitinase 3-like 1 (Chi3l1 or Brp39), predominantly by endogenous renal cells. The cognate receptor for Mcp1, Ccr2, is highly expressed on all bone marrow-derived cells; while the profibrotic receptor for Brp39, Crth2, is highly expressed on both macrophages and myofibroblasts. We found that injured kidneys from Brp39-/- mice and Ccr2-/- mice exhibit less profibrotic macrophage accumulation and interstitial fibrosis than wild-type control mice. Together, these findings have led us to hypothesize that failed tubule repair following kidney injury promotes sustained tubular cell expression of Brp39, with increased Crth2+ macrophage and myofibroblast profibrotic activation, and that the Brp39-stimulated macrophages upregulate Mcp1, leading to further Ccr2-dependent proinflammatory cell accumulation, myofibroblast activation, renal fibrosis and dysfunction. Thus, targeting the Brp39-Crth2 and/or Mcp1-Ccr2 signaling pathways after kidney injury holds great potential for the treatment of CKD progression. To test this hypothesis, we propose to first define the role of macrophage-Mcp1 expression in promoting abnormal accumulation and activation of Ccr2+ inflammatory cells in the setting of maladaptive kidney repair (Aim 1); and then determine the importance of sustained tubular cell-Brp39 expression in the profibrotic activation of Crth2+ macrophages and myofibroblasts (Aim 2). Lastly, in order to translate our understanding of these two signaling into the development of clinically relevant therapeutics, we will engineer and test two distinct dendrimer-based nanomedicines for selective targeting of proximal tubule-Brp39 expression and of interstitial macrophage-Ccr2 and -Crth2 signaling responses to slow or prevent CKD progression (Aim 3). The studies and career development/training activities in this K01 proposal are designed to equip Dr. Leyuan Xu with the technical and scientific expertise and the experience to become an independent investigator exploring the topics of CKD and its related translational medicine.